actualy is not that hard.
usualy plastic frames has metal clips on inside side under rubber and metal frames has screws inside chanel.
But it is not stric rule.
One of this two metods is used to secure frame to the door.
Remove clips or screws, inside part of rubber flip over door frame and just gently but strong push whole window out.
Be careful not to drop window to the ground while pushing it out.
It will go much easier if you start pushing at one corrner.
That is it.